add chapter 4

chapter4/tocelsius/tocelsius.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"fmt"
+	"golang-book/head-first-go/chapter4/keyboard"
+	"log"
+)
+
+func main() {
+	fmt.Print("Enter a temperature in Farenheit: ")
+	farenheit, err := keyboard.GetFloat()
+	if err != nil {
+		log.Fatal(err)
+	}
+	celsius := (farenheit - 32) * 5 / 9
+	fmt.Printf("%0.2f degrees Celsius\n", celsius)
+}